Claude Code Hooks

Execute custom scripts before/after Claude Code tool invocations.

Quick Reference

Event	When	Has Matcher
PreToolUse	Before tool execution	Yes
PostToolUse	After tool completes	Yes
PermissionRequest	Permission dialog shown	Yes
Notification	Notifications sent	Yes
UserPromptSubmit	User submits prompt	No
Stop	Agent finishes	No
SubagentStop	Subagent finishes	No
PreCompact	Before context compaction	No
SessionStart	Session begins/resumes	No
SessionEnd	Session ends	No

Basic Configuration

Add to ~/.claude/settings.json or .claude/settings.local.json:

{
  "hooks": {
    "PreToolUse": [{
      "matcher": "Bash",
      "hooks": [{
        "type": "command",
        "command": "$CLAUDE_PROJECT_DIR/hooks/validate.sh",
        "timeout": 5000
      }]
    }]
  }
}

Matcher Patterns

Pattern	Matches
"Write"	Only Write tool
"*" or ""	All tools
"mcp__*"	All MCP tools
"Bash"	Bash commands

Hook Script Requirements

#!/bin/bash
# Receives JSON via stdin: { "tool_name": "...", "tool_input": {...} }
INPUT=$(cat)
TOOL=$(echo "$INPUT" | jq -r '.tool_name')

# Exit codes:
# 0 = Success (continue)
# 2 = Block with error (stderr shown to Claude)
# Other = Non-blocking error

Common Use Cases

Use Case	Event	Example
Validate inputs	PreToolUse	Block dangerous commands
Audit logging	PostToolUse	Log all tool usage
Custom approval	PermissionRequest	Slack notification
Session init	SessionStart	Load project context

Security Checklist

• Quote all variables: "$VAR" not $VAR
• Validate paths (no .. traversal)
• Use $CLAUDE_PROJECT_DIR for paths
• Set reasonable timeouts
• Handle jq parsing errors

Troubleshooting

# Debug hook loading
claude --debug

# List registered hooks
/hooks

# Test script manually
echo '{"tool_name":"Bash"}' | ./hooks/validate.sh

Official Documentation

• https://code.claude.com/docs/en/hooks - Hooks reference
• https://code.claude.com/docs/en/settings - Settings configuration

Additional Resources

• ./references/hook-events.md - All events with input/output schemas
• ./references/configuration.md - Advanced config patterns
• ./references/security-patterns.md - Production security

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See Also: claude-code-debug for troubleshooting, claude-code-headless for CLI automation